Semiconductor device

ABSTRACT

Disclosed is a semiconductor device. The semiconductor device includes a functional circuit having a resistor formed by a plurality of polysilicon resistors, and in which the property of the functional circuit can be adjusted by trimming the resistor, and in which the polysilicon resistors are coupled in series or in parallel to each other and arranged in a direction perpendicular to one side of the semiconductor device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. Application Ser. No. 13/864, 464, filedApr. 17, 2013 which claims priority to Japanese Patent Application No.2012-101541 filed on Apr. 26, 2012, the entire disclosures of allapplications listed above are hereby incorporated by reference.

BACKGROUND

The present invention relates to a semiconductor device, and, forexample, to a semiconductor device including a polysilicon resistor.

An on-chip oscillator to be mounted in a semiconductor device isrequired to secure desired oscillation frequency accuracy under a presetoperating condition (power supply voltage, operating temperature). Avariation in a resistive element can be considered to be one of thefactors by which the oscillation frequency of the on-chip oscillator isvaried. The electrical property of a circuit element mounted in asemiconductor device, such as a resistor, is influenced by an error inthe condition of manufacturing the semiconductor device, and accordinglythe oscillation frequency also varies for every wafer and chip. In orderto secure required oscillation frequency accuracy, trimming, by which aresistance value of every chip is adjusted, is generally performed for asemiconductor device in a wafer state.

On the other hand, it is known that a value of a diffused resistormounted in a semiconductor device varies after a mold package processfor resin-sealing a chip. Japanese Unexamined Patent Publication No.1998-189875 (Patent Document 1) discloses that, in order to suppress avariation in a resistance value of a diffused resistor formed byintroducing impurities into a silicon substrate, the variation beingcaused by a piezo-resistance effect, the diffused resistor is arranged,from the periphery toward the center of a chip main body, in an areawithin one-third of the distance between the periphery and the centerthereof. Japanese Unexamined Patent Publication No. 1994-97368 (PatentDocument 2) disclosed that, in order to prevent a variation in theproperty of an element, the variation being caused by a stress generatedwhen a semiconductor chip is mold-sealed, a group of resistors and agroup of transistors are arranged in the circumferential direction fromthe peripheral portion toward the center.

PATENT DOCUMENT

[Patent Document 1] Japanese Unexamined Patent Publication No.1998-189875

[Patent Document 2] Japanese Unexamined Patent Publication No.1994-97368

SUMMARY

When a trimming resistor for adjusting the property of a functionalcircuit is formed by a polysilicon resistor, the property thereof, whichhas been adjusted in a wafer stage, varies after a mold package process,and hence it is difficult to provide a semiconductor device having arequired property. Other problems and new features will become clearfrom the description and accompanying drawings of the presentspecification.

According to one embodiment, a semiconductor device includes afunctional circuit having a resistor formed by a plurality ofpolysilicon resistors, and in which the property of the functionalcircuit can be adjusted by trimming the resistor, and in which thepolysilicon resistors are coupled in series or in parallel to each otherand arranged in a direction perpendicular to one side of thesemiconductor device.

Advantage of the Invention

According to the one embodiment, a semiconductor device can be provided,in which the property of a functional circuit, which has been adjustedby trimming a resistor, can be maintained after a mold package process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating the structure of a semiconductor deviceaccording to First Embodiment;

FIG. 2 is a circuit view of an on-chip oscillator according to FirstEmbodiment;

FIGS. 3A and 3B are circuit views of a current generating circuit and aresistor according to First Embodiment;

FIG. 4 is a layout view of the resistor according to First Embodiment;

FIGS. 5A and 5B are layout views illustrating an arrangement area for apolysilicon resistor according to First Embodiment;

FIGS. 6A and 6B are views illustrating a specific example of thearrangement area for the polysilicon resistor according to FirstEmbodiment;

FIG. 7 is a graph explaining a coefficient of resistance variation inthe polysilicon resistor according to First Embodiment, occurring when adirection in which the polysilicon resistor is arranged is changed;

FIG. 8 is a graph explaining a coefficient of resistance variation inthe polysilicon resistor according to First Embodiment, occurring when aplace where the polysilicon resistor is arranged is changed;

FIG. 9A is a view and FIG. 9B is a graph both explaining a coefficientof resistance variation in the polysilicon resistors arranged at acorner portion and a center portion of the semiconductor deviceaccording to First Embodiment;

FIG. 10 is a graph explaining a change in the coefficients of resistancevariation in the polysilicon resistor according to First Embodiment,occurring when the length thereof is changed;

FIG. 11 is a view explaining the structure of a semiconductor deviceaccording to First Variation of First Embodiment;

FIG. 12 is a view explaining the structure of a semiconductor deviceaccording to Second Variation of First Embodiment; and

FIG. 13 is a view explaining the structure of a semiconductor deviceaccording to Third Variation of First Embodiment.

DETAILED DESCRIPTION

Hereinafter, preferred embodiments will be described with reference tothe accompanying drawings. When the number of pieces and quantity arementioned in the description of the preferred embodiments, the preferredembodiments are not necessarily limited to the number of pieces andquantity, unless otherwise indicated. In the drawings of the preferredembodiments, like reference symbols and numerals are intended toindicate the same or similar parts. In the description of the preferredembodiments, duplicative description of the parts denoted with likereference symbols, etc., may not be repeated.

First Embodiment

With reference to FIG. 1, the structure of a semiconductor device LSIaccording to First Embodiment will be described.

The semiconductor device LSI includes a CPU (Central Processing Unit) 1,a RAM (Random Access Memory) 2, a flash memory 3, a register 4, a buscontrol circuit 4B, an AD converter 5B, a real-time clock 8, a clockgenerating circuit CPG, and a bus 9. The clock generating circuit CPGhas an on-chip oscillator OCO, a PLL circuit 5, an oscillator circuitOSC, and a 32-kHz oscillator circuit 7. When a crystal oscillator (notillustrated) is externally attached to the 32-kHz oscillator circuit 7,the real-time clock 8 can be made to work.

The on-chip oscillator OCO has a resistor Roco. By adjusting the valueof the resistor Roco with trimming, the oscillation frequency of theon-chip oscillator OCO is set to a desired value for every individualchip (semiconductor device LSI) formed over a wafer. The data necessaryfor the trimming is written into the flash memory 3, and the structure(resistance value) of the resistor Roco is electrically changed based onthe data read out via the register 4.

With reference to FIG. 2, the circuit structure of the on-chiposcillator OCO according to First Embodiment will be described.

The on-chip oscillator OCO has a relaxation oscillator 20, a currentgenerating circuit 21, and a reference voltage generating circuit 22.The reference voltage generating circuit 22 respectively outputs areference voltage VL and a reference voltage VH to the relaxationoscillator 20 and a reference voltage VREF2 to the current generatingcircuit 21. The current generating circuit 21 supplies a current to therelaxation oscillator 20 through an output N1, and draws a current inthe relaxation oscillator 20 through an output N2.

The relaxation oscillator 20 has comparators 23 and 24. The referencevoltage VH is applied to an inverted input terminal of the comparator23, and one end of a capacitance Coco is coupled to a non-inverted inputterminal thereof. The reference voltage VL is applied to a non-invertedinput terminal of the comparator 24, and the one end of the capacitanceCoco is coupled to an inverted input terminal thereof. A power supplyvoltage VSS is applied to the other end of the capacitance Coco. Anoutput of the comparator 23 is coupled to a set input of an RS-typeflip-flop 25, and an output of the comparator 24 is coupled to a resetinput of the RS-type flip-flop 25.

The one end of the capacitance Coco, one end f a switch SW1, and one endof a switch SW2 are coupled to a node NC. The other end of the switchSW1 is coupled to a node N1, and the other end of the switch SW2 iscoupled to a node N2. The switches SW1 and SW2 are complementarilyopened and closed by an output of the RS-type flip-flop 25, therebyallowing the capacitance Coco to be charged and discharged by thecurrent generating circuit 21. The oscillation frequency of therelaxation oscillator 23 is determined by a current flowing through theoutputs N1 and N2 of the current generating circuit 21, the capacitanceCoco, the reference voltage VH, and the reference voltage VL.

With reference to FIGS. 3A and 3B, the circuit structures of the currentgenerating circuit 21 and the resistor Roco according to FirstEmbodiment will be described.

The current generating circuit 21 illustrated in FIG. 3A has adifferential amplifier 30, the resistor Roco, p-type transistors 31, 32,and 33, and n-type transistors 34 and 35. The reference voltage VREF2 isapplied to an inverted input terminal of the differential amplifier 30,and a voltage at a node NF is applied to a non-inverted input terminalthereof. An output of the differential amplifier 30 is applied to a gateof each of the p-type transistors 31, 32, and 33, and a power supplyvoltage VDD is applied to a source of each of them. One end of theresistor Coco is coupled to a drain of the p-type transistor 31 and theother end thereof is applied with the power supply voltage VSS.

The p-type transistor 31 and the resistor Roco are coupled in series toeach other between a power supply wiring VDD (symbol of VDD means apower supply voltage and a power supply wiring, the same hereinafter)and a power supply VSS (symbol of VSS means a power supply voltage and apower supply wiring, the same hereinafter) through the node NF. Aconstant current Iref determined by the reference voltage VREF2 and thevalue of the resistor Roco flows through the resistor Roco. Agate of then-type transistor 34 is coupled to a drain thereof, and a source isapplied with the power supply voltage VSS. Agate of the n-typetransistor 35 is coupled to the gate of the n-type transistor 34, and asource thereof is applied with the power supply voltage VSS. That is,the p-type transistors 32 and 33 and the n-type transistors 34 and 35form a current mirror circuit.

A current, proportional to the constant current Iref flowing through theresistor Roco, flows through outputs N1 and N2 of the current mirrorcircuit. A current flowing out of the output N1 charges the capacitanceCoco in FIG. 2, and a current flowing in the output N2 discharges thecapacitance Coco, thereby allowing the on-chip oscillator OCO tooscillate at a desired frequency.

The resistor Roco illustrated in FIG. 3B has a structure in which aresistor R, a resistor 2R, . . . , a resistor 256R are coupled in seriesto each other. The resistor 2R has a value two times larger than that ofthe resistor R, and the relationship between the resistor R and each ofthe other resistors is the same as that. A switch is coupled at bothends of each resistor in parallel therewith. For example, a switch SW8Ris coupled in parallel to the resistor 8R, and opening and closing ofthe switch SW8R are controlled by a signal S8. This signal S8 and asignal by which opening and closing of a switch (not illustrated), whichis coupled to each of the other resistors in parallel therewith, iscontrolled, are controlled based on data stored in the resister 4illustrated in FIG. 1. Trimming of the resistor Roco is performed basedon the data, and the value of the resistor Roco is adjusted such thatthe on-chip oscillator OCO outputs a clock having a desired oscillationfrequency.

Because the clock generated in the on-chip oscillator OCO is applied toa wide range of applications, the clock is required not to vary withpower supply and temperature. For example, the on-chip oscillator OCO tobe mounted in a 160 nm process microcomputer is required that avariation in the oscillation frequency should be approximately ±3% orless over a wide range in which a power supply voltage is 1.8 V to 5.5 Vand operating temperature is −40° C. to 125° C. In particular, for theon-chip oscillator OCO required to have an oscillation frequency withhigh accuracy, it is required that a variation in the oscillationfrequency should be ±1% or less.

When represented by a value of a circuit element and a voltage, theoscillation frequency of the on-chip oscillator OCO illustrated in FIG.2 is represented as follows:

F=VREF2/(VH−VL)*1/CR  Equation 1

wherein C is a value of the capacitance Coco, R is a value of theresistor Roco, symbol “/” means division, and symbol “*” meansmultiplication, respectively. As represented in Equation 1, theoscillation frequency F is inversely proportional to the multipliedvalue of the capacitance Coco and the resistor Roco. Accordingly, itbecomes possible to achieve a target oscillation frequency F byadjusting a value of the resistor Roco with trimming.

With reference to FIG. 4, the layout of the resistor Roco will bedescribed. The resistor Roco is formed by arranging basic resistorpatterns 40 in series or in parallel to each other. The resistor pattern40 indicates polysilicon formed into a rectangular shape, and contacts41 are formed at both ends thereof. One resistor pattern 40 and anotherresistor pattern 40 are coupled together by a wiring layer via thecontact 41. In FIG. 4, 8 resistor patterns 40, by which the resistor Rlocated on the lower right side is formed, are coupled in parallel toeach other, and one end of each of the resistor patterns 40 is coupledto the power supply wiring VSS. One end of the resistor pattern 40located on the upper left side is coupled to the node NF. Because it isneeded in trimming to increase or decrease a value of the resistor Roco,some resistor patterns are inserted as a spare for the resistor 64R.

It becomes possible to achieve an oscillation frequency with highaccuracy by using a metal resistor having a high Young's modulus, suchas titanium nitride (TiN) and tungsten (W), instead of forming theresistor Roco by polysilicon. However, a mask for exposing a wafer andadditional manufacturing steps, which are needed for forming the metalresistor, are required, and further there is the problem that thepattern area of the metal resistor is increased due to the lowerresistivity thereof. On the other hand, in the case of the on-chiposcillator OCO according to First Embodiment, the resistor Roco isformed by polysilicon that is used in forming other circuit elements,such as a transistor, the step of manufacturing the wafer is notcomplicated. Further, because the resistivity of polysilicon is high,the pattern area of the resistor Roco can be more reduced than that of ametal resistor. In order to adjust the resistivity of the polysiliconresistor, p-type or n-type impurities are ion-implanted into thepolysilicon formed over the wafer.

The present applicant has studied that the aforementioned polysiliconresistor might be adopted as a trimming resistor for adjusting theproperty of a circuit formed over the wafer to a desired value. Apolysilicon resistor has good consistency with a process for forming anelement, such as a transistor, and contributes to a reduction in a chiparea. However, when a chip in which the oscillation frequency of theon-chip oscillator OCO has been adjusted to a desired value by trimmingthe resistor Roco formed by polysilicon resistors, is resin-sealed, theoscillation frequency thereof varies. This variation in the oscillationfrequency is caused because the properties of the resistor Roco and thecapacitance Coco vary due to a mold package process (a series of stepsfrom resin-sealing to reflow). In particular, in a polysilicon resistorforming the resistor Roco, the absolute value of the resistance and thetemperature coefficient vary before and after the mold package process.It is believed that this variation is caused, as one factor, by a stressapplied to the chip during the mold package process.

In order to achieve, with polysilicon, a trimming resistor by which theproperty of a circuit, such as the on-chip oscillator OCO, is adjusted,it is essential to suppress a variation in the property of a polysiliconresistor, occurring due to the mold package process. The presentapplicant has acquired the following knowledge by measuring variationsin the resistance values of polysilicon resistors in each of the moldpackage process. That is, the applicant has acquired a condition inwhich polysilicon can be adopted as a trimming resistor by appropriatelysetting an arrangement area, orientation, and shape, etc., of thepolysilicon.

With reference to FIG. 5, an arrangement area for the polysiliconresistor according to First Embodiment will be described. FIG. 5Aschematically illustrates the layout of the semiconductor device LSI.The semiconductor device LSI has a rectangular shape, and morepreferably has a square shape. Hereinafter, four sides of a rectangularshape illustrated as the semiconductor device LSI means cut sides formedby individually cutting out, with dicing, a plurality of chips formedover a wafer. This cut side is sometimes described as a “chip side”.

The semiconductor device LSI has arrangement areas 51, 52, 53, and 54for the polysilicon resistors, and arrangement prohibited areas 55, 56,57, 58, 59 a, and 59 b. The borderlines of each of the arrangementareas, which are parallel to a chip side, are defined within a regionof, from the chip side toward the inside, a distance A or more to adistance B or less. Hereinafter, the borderlines located at the distanceA and at the distance B are also described as an “outside arrangementborderline A” and an “inside arrangement borderline B”, respectively. Ineach of the arrangement areas, the borderline perpendicular to thecorresponding chip side is defined by the borderline with thearrangement prohibited area, but it is desirable that both theborderlines perpendicular to the chip side are set to be nearer to thecenter of the chip side. The arrangement prohibited areas 59 a and 59 bare set to be on the diagonal lines of the semiconductor device LSI. Thearrangement prohibited areas 55 to 58 are formed at four corners of thesemiconductor device LSI, each of which is defined as a square areawhose one side has a length of a distance C. Detail of the distances, A,B and C will be described later.

With reference to FIG. 5B, the orientation of the polysilicon resistorin First Embodiment will be described. It is assumed that: a polysiliconresistor Rv has a rectangular shape having a size of W in width×L inlength; and a current flows in a direction perpendicular to a chip sideof the semiconductor device LSI. Similarly, a current flowing through apolysilicon resistor Rh is assumed to flow in a direction parallel tothe chip side. In this case, it is defined that the polysilicon resistorRv and the polysilicon resistor Rh are arranged to be perpendicular tothe chip side and to be parallel thereto, respectively.

Each of the arrangement areas in FIG. 5A represents an area where thevalue of the polysilicon resistor arranged therein hardly varies beforeand after the mold package process. The direction of the polysiliconresistor arranged in this arrangement area is set to be perpendicular toa chip side. The arrangement prohibited area represents an area wherethe value of the polysilicon resistor arranged therein greatly variesbefore and after the mold package process. A polysilicon resistorrequired to have a highly-accurate value, such as the resistor Roco bywhich the constant current Iref (FIG. 3A) of the on-chip oscillator OCOis determined, should not be arranged in the arrangement prohibitedarea.

With reference to FIGS. 6A and 6B, a specific example of the arrangementarea for the polysilicon resistor will be described. FIG. 6A shows theresults of experiments carried out by the present Applicant. Thehorizontal axis represents the length (chip size) of one side of thesemiconductor device LSI, while the vertical axis represents the valuesof the outside arrangement borderline A and the inside arrangementborderline B. It has been known that, when the chip size is one of 4.15mm, 4.932 mm, and 5.70 mm, the value of the outside arrangementborderline A is desirably set to be 100 μm, irrespective of chip size.Also, it has been known that the value of the inside arrangementborderline B is increased with an increase in the chip size and isdesirably set to be 750 μm, 800 μm, and 900 μm.

FIG. 6B illustrates an example of the arrangement of the on-chiposcillator OCO. An I/O cell (I/O buffer) 61 including a pad 62 that isto be coupled to a lead wiring of the package by a metal wiring, such asa bonding wire, is arranged near to one chip side of the semiconductordevice LSI. The resistor Roco included in the on-chip oscillator OCO isa polysilicon resistor for trimming, and is arranged, between theoutside arrangement borderline A and the inside arrangement borderlineB, in a direction perpendicular to the chip side.

With reference to FIG. 7, a coefficient of resistance variation in thepolysilicon resistor, occurring when a direction in which thepolysilicon resistor is arranged is changed, will be described.

The horizontal axis represents the steps at which the resistance valueof the polysilicon resistor is measured. The “wafer” means that theresistance thereof is measured in a wafer state before the mold packageprocess. The “resin-sealing”, “bake”, and “reflow” mean ordinary stepsin the mold package process, respectively. The vertical axis representsa coefficient of resistance variation (hereinafter, also and simplydescribed as a “coefficient of variation”) measured in each of theaforementioned steps in the mold package process, based on theresistance value of the polysilicon resistor in the wafer state. The“horizontal” or “vertical” means, with respect to the chip side, adirection in which the polysilicon resistor is arranged. The “N+Polyresistor” or “P+Poly resistor” means a polysilicon resistor into which ahigh concentration of N-type impurities or P-type impurities have beendoped. The polysilicon resistor to be measured is arranged at a position300 μm away from the center of the chip side.

Dependency of a coefficient of resistance variation in the polysiliconresistor on a direction in which the resistor is arranged will bestudied. The graph Inv shows coefficients of variation in the values ofthe N+Poly resistor arranged in the vertical direction. The resistancevalue is increased by 0.2 to 0.3% after the resin-sealing step, and theincrease becomes approximately 0.1% after the reflow step. The graph 7nh shows coefficients of variation in the values of the N+Poly resisterarranged in the horizontal direction. The resistance value is increasedto nearly 1% after the resin-sealing step, and finally increased toapproximately 1.3%. The graph 7 pv shows coefficients of variation inthe values of the P+Poly resistor arranged in the vertical direction.The resistance value is decreased by approximately 0.4% after the reflowstep. The graph 7 ph shows coefficients of variation in the values ofthe P+Poly resistor arranged in the horizontal direction. The resistancevalue is decreased to approximately 1.7 to 1.8%.

It has been known that positive/negative of the coefficient of variationdepends on a conductive type (n-type/p-type) of the impurities dopedinto the polysilicon resistor and there is a great difference betweenthe coefficients of variation occurring when a direction in which thepolysilicon resistor is arranged is changed. It has been known that, byarranging the polysilicon resistor in a direction perpendicular to thechip side, the coefficient of variation, occurring after the reflowstep, can be suppressed to be within a range of 0.1% (doped with n-typeimpurities) to 0.4% (doped with p-type impurities). Accordingly, it ispreferable to arrange the polysilicon resistor in a directionperpendicular to the chip side.

With reference to FIG. 8, a coefficient of resistance variation in thepolysilicon resistor, occurring when a place where the polysiliconresistor is arranged is changed, will be described.

The horizontal axis represents a distance at which the polysiliconresistor is arranged, based on the chip side. The vertical axisrepresents a coefficient of resistance variation measured after thereflow step, based on the value of the polysilicon resistor in the waferstate. The shape of the polysilicon resistor is a rectangle patternhaving a size of 0.36 μm in width×5 μm in length, and the semiconductordevice LSI in which the polysilicon resistor is formed has a squareshape whose one side is 4.932 mm long.

The graphs 8 nv and 8 pv show coefficients of resistance variation inthe polysilicon resistor arranged in the vertical direction. Taking intoconsideration that the range of variation in the oscillation frequencyof the on-chip oscillator OCO is required to be ±1% or less, in the caseof the polysilicon resistor into which n-type impurities have beendoped, it is needed that a distance at which the polysilicon resistor isto be arranged is set to be within a range of 100 μm to 800 μm and acoefficient of resistance variation in the polysilicon resistor, from awafer state (i.e., a state where trimming has been completed) to a stateafter the mold package process, is suppressed to be approximately ±0.5%or less. Accordingly, it is preferable that the polysilicon resistorarranged in a direction perpendicular to the chip side is arrangedwithin a range of approximately 100 μm to 800 μm from the chip side.Further, it is preferable to arrange the polysilicon resistor near tothe center of the chip side.

With reference to FIGS. 9A and 9B, a coefficient of resistance variationin the polysilicon resistor arranged at a corner portion and a centerportion of the semiconductor device LSI will be described.

FIG. 9A illustrates positions of: a polysilicon resistor R2 arranged atthe upper left corner portion of the semiconductor device LSI; and apolysilicon resistor R3 arranged at the center portion thereof. Thesemiconductor device LSI has a square shape whose one side is L-cm long.Based on the upper left corner of the semiconductor device LSI, thepolysilicon resistor R2 is arranged at a position d2 away therefrom,while the polysilicon resistor R3 is arranged at a position d3 awaytherefrom. A polysilicon resistor R1 for comparison is arranged at aposition d1 away from the center of the left side of the semiconductordevice LSI. Each of the polysilicon resistors R1 to R3 is arranged in adirection perpendicular to the chip side on the left side of thesemiconductor device LSI.

FIG. 9B shows a coefficient of resistance variation in each of theaforementioned resistors R1 to R3 arranged in each of the semiconductordevices LSI whose one side Lc is 4.15-mm long, 4.932-mm long, and5.70-mm long. A resistance value of each of the resistors R1 to R3 ismeasured after the resin-sealing, and the basis of the coefficients ofresistance variation is a resistance value of each of the resistors R1to R3 in the wafer state. The resistor R1 is arranged in the arrangementarea for resistor, and is measured for the comparison with themeasurement results of the resistors R2 and R3. The value of theresistor R1 is hardly dependent on the value of the chip size Lc, andthe coefficient of variation is approximately 0.2% to 0.3% (in the caseof N+Poly resistor).

The value of the resistor R2 arranged at a corner portion d2 (=4 mm)away from the corner of the semiconductor device LSI is hardly dependenton the value of the chip size Lc; however, the coefficient of variationis 0.5% to 0.6%, which is two times larger than that of the resistor R1(in the case of N+Poly resistor). If the resistor Roco in the on-chiposcillator OCO is arranged in this area, a decrease in the oscillationfrequency accuracy may be caused. Accordingly, it is preferable that acorner portion is set to be an arrangement prohibited area where it isprohibited to arrange the polysilicon resistor.

The value of the resistor R3 arranged at the center portion of thesemiconductor device LSI is hardly dependent on the value of the chipsize Lc, and the coefficient of variation is approximately 0.7% (in thecase of N+Poly resister). Accordingly, it is preferable that each of thecenter portion and a position located on the diagonal lines is also setto be an arrangement prohibited area for the polysilicon resistor,similarly to the corner portion.

With reference to FIG. 10, a change in the coefficients of resistancevariation in the polysilicon resistor, occurring when the length thereofis changed, will be described.

The horizontal axis represents the length L of the polysilicon resistor,while the vertical axis represents a coefficient of resistance variationmeasured after the resin-sealing, based on the measured value in thewafer state. The measured polysilicon resistor is arranged at a position300 μm away from the center of the chip side and perpendicularly withrespect to the chip side. The coefficient of variation is more decreasedas the length L of the polysilicon resistor becomes smaller. Further,the coefficient of variation tends to be more decreased as the width Wof the polysilicon resistor is smaller. This is because, as the widthand length of the polysilicon resistor become smaller, respectively, thepolysilicon resistor is more hardly influenced by a stress occurring dueto the mold package process. On the other hand, the change in thecoefficients of resistance variation in the N+Poly resistor is smallerthan that in the P+Poly resistor. This is because, the concentration ofimpurities in the N+Poly resistor is higher than that of the P+Polyresistor, and hence the piezo-resistance coefficient of the N+Polyresistor is smaller than that of the P+Poly resistor.

The resistor Roco in the on-chip oscillator OCO is formed by arranging aplurality of basic polysilicon resistors in series or in parallel toeach other, so that the resistance value of the resistor Roco can beadjusted by trimming. For example, by making the polysilicon resistor tohave a width W of 0.36 μm and a length L of 5.0 μm, a decrease in theoscillation frequency accuracy, occurring due to a change in theresistance values resulting from the aforementioned stress, can besuppressed. The area of this resistor is smaller than that of aresistive element to be used in an ordinary analog circuit (e.g.,width×length is 1 μm×10 μm or 0.56 μm×28 μm).

Advantages of the semiconductor device LSI according to First Embodimentwill be described. A trimming resistor for adjusting the property of afunctional circuit packed in a functional unit, such as the on-chiposcillator OCO, is formed by a plurality of polysilicon resistors, andeach of the polysilicon resistors is arranged in a directionperpendicular to the chip side. By defining the direction, in which thepolysilicon resistor for trimming is oriented, in such a way, theproperty (oscillation frequency) of the functional circuit, which hasbeen adjusted by trimming in a wafer stage, can also be maintainedwithin a range in which no problem is caused in practical use, after themold package process performed subsequently.

The polysilicon resistor for trimming is arranged in a directionperpendicular to one chip side and between an outside arrangementborderline and an inside arrangement borderline respectively set atpredetermined distances from the chip side. It is more preferable toarrange it near to the center portion of the chip side. Thereby, avariation in the property of the functional circuit, which has beenadjusted by trimming, can be further suppressed. The polysiliconresistor for trimming should not be arranged at each corner portion (4corners) and further on the diagonal lines of the semiconductor deviceLSI. Thereby, it can be prevented that the property of the functionalcircuit, which has been adjusted by trimming after the mold packageprocess, may not meet a required specification.

First Variation of First Embodiment

With reference to FIG. 11, the structure of a semiconductor device LSIaccording to First Embodiment will be described.

FIG. 11 illustrates an example in which an on-chip oscillator 111 isarranged in an area (hereinafter, described as an “I/O cell region”)where an I/O cell 61 is arranged. When the semiconductor device LSI is amicrocomputer designed with 160-nm node, the height of the I/O cell 61is approximately 160 μm. This area is located near to the outsidearrangement borderline A of 100 μm, and accordingly a decrease in theoscillation frequency accuracy, occurring due to a stress in a trimmingresistor R111 comprised of the polysilicon resistors, can be suppressed.

Second Variation of First Embodiment

With reference to FIG. 12, the structure of a semiconductor device LSIaccording to Second Variation will be described.

FIG. 12 illustrates an example in which an on-chip oscillator 121, inwhich an I/O cell (not illustrated) is housed, is arranged in the I/Ocell area. The on-chip oscillator 121 houses the I/O cell and a pad 62thereof, and has both functions of an on-chip oscillator and an I/Ocell. With this structure, a change in the resistance values, occurringdue to a stress in a trimming resistor R121, can be suppressed, andlayout design of power supply wirings, in which a countermeasure bywhich the on-chip oscillator 121 is not influenced by a power supplynoise is taken into consideration, can be made easily. Further, bypacking both the functions of an I/O cell and an on-chip oscillator in asingle functional circuit, a dead space, occurring due to the design ofa floor plan for element arrangement or a wiring layout, is hardlycreated, and an effect of reducing the area of the semiconductor deviceLSI can be exerted. Furthermore, by arranging the on-chip oscillator inthe I/O cell area, the number of electrostatic protecting elements foron-chip oscillator can also be reduced, thereby allowing a synergeticeffect of reducing area to be exerted.

Third Variation of First Embodiment

With reference to FIG. 13, the structure of semiconductor device LSIconcerning variation 3 of First Embodiment is explained.

FIG. 13 illustrates an example in which: of the circuit elements thatform an on-chip oscillator, resistors and capacitances, each of which islikely to be influenced by a variation in the property occurring due toa stress, are arranged in an area 132 provided in the I/O cell area; andother circuit elements are arranged in an area 131 provided furtherinside (toward the center of the chip) the inside arrangement borderlineB. By arranging an on-chip oscillator separately in such a way, itbecomes possible to suppress a decrease in oscillation frequencyaccuracy while flexibility in arrangement is being secured.

First Embodiment and the variations thereof are not limited to theon-chip oscillator OCO, but can be applied to functional circuits whosecircuit property can be adjusted by trimming a polysilicon resistor in awafer state. Such functional circuits can be exemplified by a flash typeAD converter circuit, subranging type AD converter circuit, R-2R type DAconverter circuit, and power supply circuit, etc.

It should be understood that the embodiments disclosed herein areexemplary in all points and do not limit the invention. The scope of theinvention is defined not by the above description but by claims and itis intended that the scope of the invention includes equivalents ofclaims and all modifications within the scope of claims.

What is claimed is:
 1. A semiconductor device comprising: an on-chiposcillator including a resistor capable of being trimmed for adjustingan oscillation frequency of the on-chip oscillator, the resistorincluding a plurality of polysilicon resistors which are coupled inseries or in parallel to each other and arranged in a directionperpendicular to one side of the semiconductor device, and a flashmemory storing a data necessary for trimming the resistor.
 2. Asemiconductor device according to claim 1, further comprising: aregister for storing the data received from the flash memory, wherein aresistance value of the resistor is electrically changed based on thedata in the register.